A lead brick and two rubber bands can have good SQ at 126db, the level they use when judging most SQ competitions. Try to make a SoloX sound good at louder listening levels, as is more likely the case with someone running a solox daily. Or most of these SPL oriented subs for that matter.
I always have to wonder, if BTL's can sound so good, and are clearly solid SPL subs, why does Fi bother making any other subs at all? //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif Its a real popular trend these days to run a full SPL sub in a daily system, and then claim it has solid SQ. I have to wonder how many of these guys really know what a really good sounding system sounds like.
Not saying the BTL is a full SPL sub only. It can be configured abit differently, unlike most of these other subs. But it will never be a Velodyne, or even IDQ.